The Kimoto Gravity Well, or KGW, is a difficulty-readjustment algorithm originally developed by Dr. Kimoto Chan for Megacoin.
In the standard bitcoin difficulty readjustment scheme, the DIFFICULTY is readjusted every 2016 blocks. This scheme proved unsatisfactory to those concerned about the rise of MULTIPOOLs. With KGW, difficulty is readjusted every block.
As of March 2014, there is some controversy around a claimed exploit in KGW.